Polygraph tests done on main accused Sanjay Roy and Sandeep Ghosh, former principal of RG Kar medical college and hospital, Kolkata. Meanwhile, CBI teams grill Sandeep Ghosh for over 100 hours. The Special Court in Kolkata has granted permission to the CBI to carry out a polygraph examination on Sanjay Roy, the primary suspect in the horrific rape and killing of a young doctor earlier this month. The same court had granted permission for the Central Bureau of Investigation's (CBI) request to conduct the test on Sandip Ghosh, the controversial former principal of R.G. Kar Medical College and Hospital, along with seven others in relation to the case.
A polygraph test, commonly known as a lie detector test, is conducted to determine whether an individual is being truthful or deceptive based on physiological responses to certain questions. Although the accuracy and reliability of polygraph tests are debated, they are sometimes used in criminal investigations, employment screenings, and other legal contexts.
Process of a Polygraph test on an accused
Polygraph is a tool or process utilized to monitor and document various physiological indicators of an individual suspected of committing a crime. Italian criminologist Cesare Lombroso first employed the test in the 19th Century.
During the test, the accused is interrogated with questions that can affect their blood pressure, pulse, respiration, and skin conductivity, which can change when dishonest answers are given.
The accused is monitored using cardio cuffs or sensitive electrodes to track blood pressure, pulse, and other variables.
Getting court approval for a polygraph test is a complicated process. In such cases, the court only approves the test if the individuals being tested give their consent.
Additionally, it is mainly used by investigative organizations to uncover the truth, and its conclusions are not admissible as legal evidence.
How the polygraph test is done?
Prior to the polygraph examination, the suspect must complete a set of tests. It usually starts with an initial round of testing where the individual is questioned by the authorities, which can serve as a reference point.
In the next stage, the defendant is prompted to intentionally deceive in order to enhance the precision of the process. Referred to as the 'stim test', it can also induce nervousness and anxiety in the accused.
The test is considered successful if the physical reactions to the diagnostic questions exceed those during the relevant questions.
Pre-Test Interview is the key…
The examiner will have a detailed conversation with the accused.
The accused is informed about the procedure, the types of questions they will be asked, and how the polygraph works.
The examiner may establish a baseline for the person's physiological responses by asking neutral, non-threatening questions.
Explanation of the equipment
The accused is connected to the polygraph machine via sensors placed on their body. The accused is reassured that the machine records physiological responses and cannot directly determine truth or falsehood. These sensors measure physiological changes such as:
Heart rate
Blood pressure
Respiratory rate
Sweat gland activity (Galvanic skin response)
Control Questions
Control questions are used to establish the baseline physiological responses of the accused. These questions are neutral, unrelated to the investigation.
For example, the examiner might ask, "Is your name John?" or "Are you sitting down?"
Relevant questions
The examiner asks the key questions related to the crime or situation under investigation.
These questions are specific to the accused's actions and involvement. For instance, "Did you steal the money?" or "Were you at the scene of the crime?"
Comparison of responses
The physiological responses to the relevant questions are compared with those to the control questions. Deviation in physiological responses (like increased heart rate or sweating) during relevant questions may indicate deception.
Post-Test interview
After the polygraph test is completed, the examiner discusses the results with the accused.
The examiner may confront the accused with any deceptive responses and ask for explanations.
Legal considerations
Polygraph tests are used as investigative tools rather than conclusive proof of guilt or innocence.
Admissibility in Court: The results of a polygraph test are generally not admissible in court in many jurisdictions because they are not considered scientifically reliable.
Voluntary Participation: An accused person typically must agree to take the test voluntarily.
What does the Indian law say about polygraphs?
Article 20 (3) of the Indian Constitution protects against self-incrimination and gives the accused the freedom to choose for the test or to reject it.
No accused can be compelled to undergo the test. Importantly, forcing an accused to undergo the test is considered a violation of Article 20 (3).
How accurate is a polygraph test?
While a polygraph test can measure arousal, causer by anxiety, posttraumatic stress disorder (PTSD), nervousness, fear, confusion, hypoglycemia, psychosis, depression, or other factors, it cannot measure lies accurately.
These are not scientifically proven to be 100 per cent accurate.
Success rate of polygraph tests in assault on women cases
The success rate of polygraph tests, particularly in cases involving sensitive issues like assault on women, varies significantly and is a matter of debate. Several factors influence the accuracy of polygraph results, including the skills of the examiner, the emotional state of the person being tested, and the specific context of the case.
Key points on Polygraph accuracy
Polygraph tests have reported accuracy rates ranging from 60% to 90% in detecting deception, according to various studies. The American Polygraph Association claims a higher accuracy rate of around 80% to 90% when administered properly. However, independent studies and critics often place the accuracy rate much lower, around 60% to 70%.
Challenges in assault cases
Emotional Impact: In cases involving assault on women, emotions like fear, anxiety, or trauma can affect physiological responses, potentially complicating the interpretation of the polygraph results. Even truthful individuals may exhibit heightened stress, which could be mistaken for deception.
Psychological State: Victims of trauma or those accused of serious crimes may exhibit unusual physiological responses due to the gravity of the situation, making the polygraph less reliable.
False Positives/Negatives: The risk of false positives (labeling truthful people as deceptive) or false negatives (failing to detect deception) can be higher in emotionally charged cases like assaults.
What experts say about the polygraph tests?
Many legal and psychological experts criticize the reliability of polygraphs, especially in sensitive cases. Courts in many countries, including the U.S. and India, often do not accept polygraph results as admissible evidence because of the potential for error.
Psychological Countermeasures: A skilled individual may intentionally try to manipulate their physiological responses during the polygraph test, complicating the results.
Real-world application in assault cases
In assault on women cases, polygraph tests are often used as an investigative tool rather than as conclusive evidence. The test might be used to support the investigation by narrowing suspects or assessing credibility but rarely forms the sole basis for determining guilt.
Polygraph tests in cases involving assault on women have a variable success rate due to the complex nature of human emotions and physiology. While the polygraph can be useful in investigations, it is not a definitive or fool-proof method, and its results should always be interpreted with caution, especially in such sensitive cases.
